part of this might be the modern drivetrain giving you a few extra cm up and out with those bars and brifters. here is plan D for you:

Put all the original parts on the 85 + new decals.
put the modern drivetrain on the 84.

you might end up with two bikes that fit just perfectly. (or you might end up with two bikes that fit just imperfectly... there is an element of risk in this method)